A general wireless communication system performs data transmission and reception through one downlink (DL) band and one uplink (UL) band corresponding to the downlink (in case of a frequency division duplex (FDD) mode), or divides a predetermined radio frame into uplink time unit(s) and downlink time unit(s) in a time domain and performs data transmission and reception through the uplink and downlink time units (in case of a time division duplex (TDD) mode). A base station (BS) and a user equipment (UE) transmit and receive data and/or control information scheduled in a predetermined time unit, for example, a subframe unit. The data are transmitted and received through a data region configured for uplink and downlink subframes, and the control information is transmitted and received through a control region configured for the uplink and downlink subframes. To this end, various physical channels carrying radio signals are configured in the uplink and downlink subframes.
Meanwhile, in the recent wireless communication system, the carrier aggregation (or bandwidth aggregation) technology, which uses greater uplink and downlink bandwidths by aggregating a plurality of uplink and downlink frequency blocks, has been discussed to use a wider frequency band.
FIG. 1 is a diagram illustrating an example of communication performed under a multi-carrier status.
A multicarrier system or carrier aggregation system refers to a system that together aggregates a plurality of carriers having a bandwidth smaller than that of a target band to support a broadband. The carrier aggregation technology is different from the orthogonal frequency division multiplexing (OFDM) technology in that downlink or uplink communication is performed using a plurality of carrier frequencies. In the OFDM technology, downlink or uplink communication is performed by carrying a basic frequency band, which is divided into a plurality of subcarriers, in one carrier frequency. When a plurality of carriers having a bandwidth smaller than that of a target band are aggregated, for backward compatibility with the system according to the related art, a bandwidth of aggregated bands may be limited to a bandwidth used in the system of the related art. For example, the LTE system according to the related art supports bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz, and the LTE-A system evolved from the LTE system may support a bandwidth greater than 20 MHz by using the bandwidths only supported by the LTE system. Alternatively, the LTE-A system may support carrier aggregation by defining a new bandwidth regardless of the bandwidth used in the system according to the related art. Multicarrier refers to a terminology that may be used together with carrier aggregation and bandwidth aggregation. Also, carrier aggregation refers to both contiguous carrier aggregation and non-contiguous carrier aggregation. For reference, if one component carrier (CC) is only used for communication in a TDD mode, or if one UL CC and one DL CC are only used for communication in a FDD mode, this communication corresponds to that performed under a single carrier situation (non-CA).